Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, and a monitoring camera, or an image pickup apparatus such as a silver-halide film camera.
Description of the Related Art
In recent years, an image pickup apparatus using a solid-state image pickup element has high functionality and a small size as an entire apparatus. As an image pickup optical system used with such image pickup apparatus, a zoom lens having a high zoom ratio, which is short in total length of the zoom lens, small in size, and bright with a large aperture has been sought for.
As a zoom lens that satisfies those requirements, there has been known a positive-lead type zoom lens including, in order from an object side to an image side, first, second, and third lens units having positive, negative, and positive refractive powers, and a rear lens group that follows, which includes at least one lens unit. As the positive-lead type zoom lens, there has been known a four-unit zoom lens including, in order from the object side to the image side, four lens units having positive, negative, positive, and positive refractive powers. In Japanese Patent Application Laid-Open No. 2007-328006, a positive-lead type four-unit zoom lens in which the second lens unit and the fourth lens unit are configured to move during zooming is disclosed.
As the positive-lead type zoom lens, there has also been known a five-unit zoom lens including, in order from the object side to the image side, lens units having positive, negative, positive, negative, and positive refractive powers. In Japanese Patent Application Laid-Open No. H09-325274, a five-unit zoom lens in which the second lens unit to the fifth lens unit are configured to move during zooming is disclosed. Moreover, in Japanese Patent Application Laid-Open No. 2012-47814, a five-unit zoom lens in which the second lens unit to the fourth lens unit are configured to move during zooming is disclosed.
The positive-lead type four-unit zoom lens and five-unit zoom lens described above are relatively easy to realize the high zoom ratio while downsizing an entire system. However, in order to obtain high optical characteristics while realizing a large aperture ratio and the high zoom ratio, it is important to appropriately set the refractive powers of the respective lens units forming the zoom lens, movement conditions of the respective lens units during zooming, and the like.
In addition, it is important to appropriately set a position of an aperture stop, lens structures of the lens units on the object side of the aperture stop, and the like. For example, it is important to appropriately set the refractive power and the lens structure of the first lens unit, an imaging magnification of the second lens unit for magnification varying, and the like. When those structures are not appropriately set, it becomes difficult to obtain the high optical characteristics over the entire zoom range while realizing the large aperture ratio, a long focal length at a telephoto end, and the high zoom ratio.